Session: MF-24-01 Materials and Fabrication for Refining-1

Paper Number: 152592

152592 - Evaluation of Welds Produced by No Backing Gas - Gas Tungsten Arc Welding With High Silicon Contained Type 347 Stainless Steels Solid Filler Rod 

Abstract: 

For fabrication and erection of piping made of low alloy steels, stainless steels (SS) and nonferrous alloys, single sided welding from external side is standard practice due to limited accessibility of welding work from internal side. Therefore, back shielding and maintenance by inert gas e.g., argon, nitrogen, and their mixture for the first few welding layers are usually required. Because back shielding provides good weldability due to fluidity of molten metal and prevents oxidation of weld metal and heat affected zone which may cause deterioration of corrosion resistance and mechanical properties of welds.

In order to save consumption of inert gas for back shielding, physical isolations are placed inside piping for the joint and the adjacent areas to be welded to make a chamber for inert gas purging, instead of inert gas purging for the whole piping length. However, placing the isolations before welding and removal of them after welding are sometimes impractical due to piping layout and construction sequence such as closure joints. To solve this issue, welding procedures for omission of back shielding, such as use of flux cored welding filler rods for gas tungsten arc welding (GTAW) or high silicon contained welding wires for gas metal arc welding in short circuit mode (GMAW-S), had been developed and achieved the objective to some extent. These practices, however, require special training and qualifications for welders, closely dimensional tolerance for fit-up, and special welding power source. Also, welding quality such as remaining slag, discoloration of welds or spatters on piping internal is sometimes an issue. These shortcomings make us hesitate to apply such welding procedures.

To make up for these shortcomings, high silicon contained solid welding filler rod had been introduced to austenitic SS Type 304L and 316L, and Cr-Mo steel Grade P5 and P9 welding by no backing gas (NBG) GTAW, and mockup tests had been conducted and the properties of the welds had been studied by comparison to the welds produced by the other welding procedures such as GTAW using solid filler rod with back shielding (conventional procedure), GTAW with flux cored filler rod without back shielding, and GMAW-S using high silicon contained solid wire without back shielding. Consequently, NBG GTAW has been implemented to piping fabrication and erection for Type 304Lin oil and gas industries since 2023.

To expand application ranges of NBG GTAW in oil & gas industries, high silicon contained Type 347 filler rod for GTAW was introduced to stabilized SS welding, and the properties of the welds by NBG GTAW had been studied by comparison to the welds produced by the other welding processes. This paper discusses and evaluates the potential of NBG GTAW for stabilized SS applications.

Presenting Author: Atsushi Takahashi JGC Corporation

Presenting Author Biography: Atsushi Takahashi has been working for JGC CORPORATION since 2006 and assigned as Chief Engineer Welding since 2019, and been in charge of developing welding requirements for EPC project, welding and casting related trouble shooting, providing educational programs of welding engineering and welding activity at fabrication shop and construction site, and carrying out welding related R&D programs.
He is a deputy chairman of Chemical Plant Welding Research Committee in Japanese Welding Engineering Society since 2022.

Authors:

Atsushi Takahashi JGC Corporation
Bin Zhou JGC CORPORATION